Microbial Activity

As already noted, the production of fermented foods shares many unit operations with other types of food processing, all of which can contribute to product safety. The unique feature of food fermentations, however, is the central role that microbial activity plays in the overall process, contributing a number of desirable properties such as improved product shelf life, increased safety, and improved flavor or texture. In developed countries today, the availability of modern food preservation techniques, such as an efficient cold chain, have diminished the significance of fermentation as a food preservation technology, although it remains of major importance in developing countries.

Improvements in food safety arising from microbial activity during fermentation are largely due to lactic acid bacteria (LAB), which are a group of organisms that predominate in the majority of fermented foods. Their growth and metabolism inhibit the normal spoilage flora of the food material and any bacterial pathogens that it may contain. This inhibition can act in two ways: It can slow or arrest growth of the organism, or it can inactivate or kill the organism. Both procedures can result in an improvement in safety. With toxigenic pathogens, the inhibition of growth can effectively ensure safety, assuming that initial numbers are below those necessary to produce levels of toxin that can cause illness. With infectious bacterial pathogens, slowing or preventing growth may be insufficient to guarantee safety because the infectious dose of some pathogens can be very low. Inacti-vation or killing of bacteria does occur, but even quite high levels of inactivation still may not be sufficient to eliminate risk entirely. This will depend on factors such as the pathogen concerned, its initial numbers, and its physiological state.

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